"Doctors told us that he has died then we came to know. He fell sick after radiation exposure. On Friday he began coughing so doctors shifted him to ICU (Intensive Care Unit)," said Ajit Kumar, relative of Rajender.
Four other radiation exposure patients are still in AIIMS.
Ten sources of Cobalt-60 had been discovered in the market.
Cobalt-60 is a radioactive isotope of cobalt, which is a hard, lustrous, grey metal. It is used in cancer therapy machines and other medical equipment.